Medium pH and Leaf Nutrient Concentration Influence Rust Pustule Diameter on Leaves of Dry Beans

Abstract

Nine bean cultivars/lines (Phaseolus vulgaris L.) were grown in three soils/rooting media at pH values of 7.9, 6.5, and 5.8 in greenhouse, growth chamber, and field experiments to evaluate the leaf reaction of the plants to a Nebraska bean rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus] isolate US85-NP-10-1. Significant differences were observed for rust pustule diameter between cultivars/lines grown in the three growth media. Plants grown in the medium at pH 5.8 showed significantly larger rust pustule diameters than those of plants grown at pH 6.5 or 7.9. A significant interaction occurred between growth medium and cultivars/lines for the rust reaction. Concentrations of Cl and Mn in leaves were positively correlated with rust pustule diameter. In contrast, concentration of K in leaves was negatively correlated with rust pustule diameter. Plant breeders attempting to improve beans for rust resistance must consider the growth medium pH in evaluating intensity and severity of rust symptoms on leaves.